Salinity contamination of soils and aquifers from exposure to high amounts of saltwater can cause adverse and long lasting impacts as salt accumulates or disassociates, leaving sodium ion particles that raise the sodicity of soil and potentially reduce soil texture. The accumulation of saltwater in soils can cause damage by destroying soil structure and permeability. Seed germination may be reduced in the presence of high concentrations of soluble salts, which limit a plant's ability to uptake water. With sufficient concentrations, salt-contaminated soil can lose its ability to support agricultural crops and other vegetation. Over time this may further contribute to erosion.
Recent trends in the field of oil and gas drilling include the use of hydraulic fracturing, which is commonly referred to as fracking. Hydraulic fracturing is a process employed to stimulate a natural gas, oil, or geothermal energy well to maximize the extraction of resources from the well. Generally, hydraulic fracturing involves injection of massive amounts of fluids, such as saltwater, into a well at high pressure to create fractures in rock formations, such as shale, that contain subterranean hydrocarbon reservoirs. Products extracted from a typical oil well involving hydraulic fracturing are crude oil and natural gas, along with the injected saltwater, which becomes an unwanted byproduct of the process. Over the production lifetime, the percentage of saltwater from a well producing oil or gas increases, and a newly-drilled well can initially produce one barrel of saltwater for every two barrels of hydrocarbons extracted. Over time, that ratio can grow to 10 barrels of saltwater for every barrel of hydrocarbons. The water extracted from such wells can easily contain over 250,000 parts per million of various types of salts, nearly equal to the waters of the Dead Sea and almost 10 times the salinity of ocean water.
Oil and gas well operators are required to properly dispose of the saltwater by-product in an environmentally responsible manner. Saltwater is typically disposed of in one of three ways. One way involves using the saltwater by-product to enhance oil production by injecting the saltwater back into an oil-producing formation. Another approach involves evaporation of water content to produce solid salt that can be collected. In a third approach, saltwater may also be injected into an underground formation that contains a natural saline aquifer. This third approach is termed saltwater disposal (SWD) and is the predominant method of disposal. Before either of the second (evaporation) or third (SWD) methods take place, saltwater is stored at the production site in a handling facility that may be a tank, pit, or pool, and transfer of saltwater to a disposal site is undertaken either by tanker truck or pipeline.
There are significant challenges with managing SWD, as indicated by the current assessment of oil and gas production development in the North Dakota Bakken Formation. Well operators currently inject around 468,000 barrels of saltwater a day into saltwater disposal sites related to the Bakken drilling activity. Future development of this production could require approximately 1,600 additional SWD wells, which currently can be built for $2 million to $3 million per well. For the next 50 to 60 years, these wells could potentially utilize roughly 10,000 barrels of saltwater per day of operation, creating a significant increase in saltwater to be disposed of. With the need to store saltwater quantities of this magnitude at handling facilities and transfer those quantities to SWD wells, the risk for potential leakage or spillage into surrounding soils and aquifers is a major concern.
While spillage of saltwater at an active production site can lead to significant soil contamination, these events are often easier to monitor and therefore can be quickly addressed. The greater risk of soil contamination, especially to rangeland and cropland, occurs both between the production location and a SWD site, and at the SWD site itself. This is especially true for saltwater transfer by pipeline, and storage in holding tanks, either above or below ground, as breaks or leaks can go undetected for an extended period. This can lead to significant long-term effects on soils, aquifers, rangeland, and cropland.
The unplanned release of saltwater brine resulting from truck and/or pipeline transport of brine, leakage from containment ponds associated with active oil and gas drilling, and at SWD sites presents a host of contamination problems with wide-ranging effects on soils, vegetation, crops, livestock, and people. For example, unintended releases of saltwater brine have the capacity to infiltrate soils and sufficiently alter its pH so as to deteriorate crop productivity. Further, if the infiltration is sufficient and sustained for a period of time, in extreme cases it can lead to a horizontal movement in soils resulting in an expansion in the contamination area and causing a wide-ranging impact cropland. Under such situations this can also lead to the contamination of groundwater supplies and present a threat to drinking water for both humans and animals. Episodes of excessive or prolonged precipitation can further exacerbate this problem if undetected.